Biomechanics of the Fibrillar Adhesive System in Insects James Michael Rex Bullock

168 Pages·2010·10.55 MB·English

Biomechanics of the Fibrillar Adhesive
System in Insects

James Michael Rex Bullock

Biomechanics of the Fibrillar Adhesive
System in Insects

James Michael Rex Bullock

Clare College

Supervised by Dr Walter Federle
This dissertation is submitted for the degree of
Doctor of Philosophy

Cambridge 2010
James M. R. Bullock, Biomechanics of the fibrillar adhesive system in insects
University of Cambridge, 2010
DECLARATION

This dissertation is submitted for the degree of Doctor of
Philosophy. It is the result of my own work and includes nothing
which is the outcome of work done in collaboration except where
specifically indicated in the text and acknowledgements. It is not
substantially the same as any previous material submitted for a
degree at any other University. This thesis totals 151 pages
(including bibliography and appendices) and does not exceed the
prescribed word limit.

Cambridge, 30th September 2010

James Bullock

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ACKNOWLEDGEMENTS

To my supervisor, Walter Federle, an enormous debt is owed. His
help and guidance have been more than critical to the success of all
that is contained within this thesis and his constant supply of ideas
and inspiration have made him one of the best supervisors one
could have, regardless of the field of research.

Uncountable thanks are due to all current and honorary members
of the Cambridge Insect Biomechanics workgroups. It has been an
immense privilege to have studied and worked with you; Ulrike
Bauer, Holger Bohn, Christofer Clemente, Kristien de Clercq, Jan-
Henning Dirks, Patrick Drechsler, Thomas Endlein, Nanna Evers,
Jamie Gundry, David Labonte, Li Ming-he, Karin Moll, Sean Ng,
Anne Peattie, Gregory Sutton, Filip Szufnarowski, Dan Thornham,
Kerstin Tüchert and Yanjia Gao.

Many thanks go to Clare College and the Department of Zoology,
who have both provided me with an exceptionally creative and
friendly environment within which to live and work. In particular
Sue Goodbody and Linda Wheatley deserve much credit.

Thanks to my advisors, Simon Laughlin and Ullrich Steiner, to my
examiners, Jon Barnes and Simon Maddrell, and to the other
members of the Department of Zoology that I have worked with
during the course of my PhD, including Malcolm Burrows, Charlie
Ellington, Felix Evers and Heather Whitney. Additionally I would
like to thank the members of the Cambridge Engineering
Department (Mechanics, Materials and Design Division),
Nanoscience Centre and Multi Imaging Centre for technical help
concerning several areas of this work.

Importantly thanks must go to Christofer Clemente, Saul
Dominguez, Patrick Drechsler, Andreas Eckart, Thomas Endlein,
Nanna Evers and Filip Szufnarowski for the initial and continued
development of the LabVIEW motor control programmes and force
feedback set-up. I would specifically like to express my deep
gratitude to Christofer Clemente and Thomas Endlein for their
continual guidance, advice and help with many of the technical and
scientific aspects of this work.

Thanks to Dan Thornham and all at the Telamba Homestay in
Brunei Darussalam for the indispensable guidance and incredible
hospitality I received during my time spent working in the field.
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This thesis was funded by research grants from the UK
Biotechnology and Biological Sciences Research Council and the
Cambridge Isaac Newton Trust. Additional funding was received
from Clare College and the Cambridge Philosophical Society.

And to my family, Michael Bullock, Felicity Bullock, Charlie
Bullock and Payel Das, who have given me constant love and
support, everything else is owed.

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ABSTRACT

Biomechanics of the fibrillar adhesive system in insects
- James Michael Rex Bullock

Many animals are able to scale smooth surfaces using adhesive
structures on their feet. These organs are either soft pads with a
relatively smooth surface or dense arrays of microscopic adhesive
hairs with both designs having independently evolved in diverse
taxa of arthropods and vertebrates. Biological adhesive pads out-
perform conventional adhesives in many respects, making them
important models for biomimetics. Hairy pads have attracted
particular attention, because it has become feasible to fabricate
similar synthetic microstructures. Nevertheless, the detailed
performance and functional properties have not been characterised
for any natural fibrillar adhesive system, and many fundamental
aspects are still not understood. The aim of this thesis was therefore
to investigate the fibrillar adhesive system of leaf beetles as a
model.
To investigate the functional implications of hairy pad design,
the attachment performance between hairy pads of the leaf beetle
Gastrophysa viridula and smooth pads of stick insects (Carausius
morosus) was compared. Adhesive and frictional stresses were
found to be similar in smooth and hairy pads, inconsistent with
contact splitting theory, which predicts higher adhesive stresses for
fibrillar adhesives. Hairy pads showed a greater direction-
dependence of friction forces than smooth pads, confirming the
importance of the asymmetric design of individual setae for
effortless detachment. Experiments with contaminating particles
also showed that hairy pads removed contamination more rapidly
and efficiently than smooth pads. Self-cleaning ability had not been
previously documented for adhesive organs of insects. To
investigate to what extent the hairy system is able to compensate
for surface roughness, whole-body attachment forces were
measured for varying roughness levels. Attachment was reduced
for all length scales of surface roughness, but in particular for
asperity sizes smaller than the diameter of individual seta tips.
Leaf beetles possess adhesive pads on three tarsal segments,
which vary in setal morphology. However, the functional
implications of this variation are unknown. The mechanical and
adhesive properties of individual pads were therefore tested and
their use during climbing observed. Proximal pads were shown to
be stiffer than distal pads, conferring stability during pushing. In
contrast, the softer distal pads allowed better attachment to rough
surfaces. Hence the morphological variation is explained by an
effective division of labour between the pads. To investigate an
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extreme example of pushing in a hairy system, pad use was studied
during jumping in flea beetles. The pushing forces needed during
take-off were exclusively produced by the proximal pads, again
confirming the division of labour. To characterise the effects of
different hair morphologies and to understand how individual
setae contribute to array and whole-animal performance, single
hair forces were measured using a glass capillary cantilever. Male-
specific discoidal hairs were shown to be both stiffer and more
adhesive than pointed and spatula-tipped setae, likely affecting
overall pad stability and attachment.
This thesis has shown that hairy pads are similar to smooth
pads in the magnitude of adhesive stress supported yet outperform
them in detachability and self-cleaning. It was also demonstrated
that there are considerable differences in design and performance
even within setal arrays of the same insect, indicating the
limitations of general models of fibrillar adhesion and underlining
the importance of specialised adaptations.

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